Chap 8: Backbone Networks

Question 1

Layer 2 SWITCH

Answer 1

Forwards messages based on their data link layer address.
Use the data link layer address or MAC address to forward packets between network segments.
They connect the same or different types of cable.
Enable all ports to be in use simultaneously by managing paired combinations of ports as separate point-to-point circuits.

Question 2

Layer 2 SWITCH

Answer 2

“Learns” addresses.
Builds a forwarding table after it is first turned on.
Retransmits to all ports (except to the one from which it was received) only for a packet with a destination address not already in the forwarding table. The resulting ACK from the destination computer (that recognized its address) is then used by the layer-2 switch to add the new port number and address to the forwarding table.

Question 3

Layer 3 SWITCH

Answer 3

Operate at the network layer, and connect two or more network segments by using the IP address instead of the MAC address for routing purposes.
Strips off the packet’s layer 2 information and works with the layer 3 information.
Will select what should be forwarded on to reduce the traffic volume on the BN.

Question 4

Layer 3 SWITCH

Answer 4

Switches switch messages on the basis of their network layer address (TCP/IP).
ROUTER switches (layer 2 switches) messages on the basis of data link layer addresses (Ethernet).
Can replace routers.
Active ports/faster transmission.

Question 5

ROUTERS

Answer 5

Devices that operate at the network layer.
Cconnect two or more network segments that use the same/different data link protocols but the same network protocol.
Good for different DL protocols: Ethernet & Token Ring but same Network protocol: TCP/IP.
Can choose best route between networks.

Question 6

3 technology layers important in BN Design

Answer 6

1. access layer
2. distribution layer
3. core layer

Question 7

Access Layer

Answer 7

Closest to the users.

Technology used in the LANs attached to the BN (wireless Ethernet)

Question 8

Distribution Layer

Answer 8

Part of BN that connects the LANs together

Question 9

Core Layer

Answer 9

connects the different BNs together, often from building to building.

Question 10

Routed Backbone

Answer 10

move packets along the backbone based on their network layer address.
Can be used at core layer or distribution layer

Question 11

Switched Backbone

Answer 11

Most common in the distribution layer.

Use star topology with one switch at its center connecting a series of LANs.